In this episode, I’ll discuss a review article that identifies the most significant rifamycin-opioid interactions.
Opioids have a narrow therapeutic index and many undergo metabolism by the CYP450 enzyme system. Rifamycins such as rifampin and rifabutin have the potential to induce CYP450 enzymes are thereby interfere with the therapeutic effects of opioids.
A group of authors recently published a systematic review in the journal Pharmacotherapy looking at clinical outcomes of concomitant rifamycin and opioid therapy.
The review analyzed 12 articles that studied primarily rifampin use and some rifabutin use with 7 different opioids.
The authors made the following conclusions:
Decreased effect of opioids with concomitant rifampin therapy manifested as withdrawal in numerous patients on methadone and a decreased analgesic effect from tramadol, morphine, and, most notably, oxycodone.
Only the combinations of rifampin with buccal fentanyl and rifabutin with buprenorphine and methadone were found to have no clinically measurable interaction.
Available literature suggests that a decrease in opioid clinical effects is appreciated with concomitant rifamycin therapy.
Pharmacists should be alert for this interaction whenever rifamycins are started in a patient on opioids, especially methadone, tramadol, morphine, and oxycodone. Depending on the opioids involved, adjustments to analgesic regimens will be necessary when rifamycins are started. Management options include increasing the opioid dose or changing the opioid to one less likely to interact, although the systematic review did not identify a preferable management strategy.
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